An engine control system of this kind has oil pressure sensing means for sensing the hydraulic pressure of the power steering system. The engine control system, when detecting a hydraulic pressure higher than a predetermined pressure, forces the engine to increase its speed of rotation so as to prevent the engine from stopping when the power steering system is in use. Such an engine control system is known from, for instance, Japanese Unexamined Patent Publication No. 52-53328.
Since oil utilized by the power steering system increases in viscosity while the engine is cold, and, therefore, the volume of oil flowing in oil passages is undesirably reduced, oil pressure can be detected as being high as the power steering is working. In this case, the engine controlled by the conventional engine control system is, when required to increase output power, unnecessarily forced to generate an excess output torque. This results in increased consumption of fuel and a deterioration in emission control.